1. Field of the Invention
The present invention relates to an image processing apparatus which generates and displays a stereoscopic image of a blood vessel or the like from a plurality of medical images at different imaging angles.
2. Description of the Related Art
As shown in FIG. 19, there is available a technique of designating a plurality of anatomically identical points from at least two medical images, typically X-ray images, at different imaging angles, and constructing a three-dimensional blood vessel image from the positional relationship between the designated points. These two X-ray images are preferably obtained in phase with the heart, as shown in FIG. 20. Images obtained in different cardiac phases differ in the three-dimensional positions of feature regions with the movement of the heart. This contradicts the major premise of the acquisition of a geometrical relationship, and hence makes it impossible to perform accurate stereoscopic construction.
As imaging methods, the following three techniques are mainly known:
a) performing imaging from one direction, rotating an imaging system, and performing imaging from another direction at a different time;
b) repeatedly performing imaging while continuously rotating an imaging system, as shown in FIGS. 21A and 21B; and
c) simultaneously obtaining two images by imaging at the same time using a biplane system having imaging systems of two systems.
The method c) is most preferable because it can perform imaging at the same time, but cannot be practiced by facilities which have no biplane system. The method a) is the most general imaging method.
The method b) is an imaging method which has recently attracted attention. This is because the method allows to simultaneously observe the stereoscopic structure of a blood vessel and its movement. The method allows to extract two suitable images from many images. The operator displays the two extracted images side by side in the same window and designates corresponding points.
According to the method b), blood vessel branches overlap depending on extracted images, resulting in difficulty in designating corresponding regions. When branches of a blood vessel run in a complicated manner as in the case of the left coronary artery, in particular, branches frequently overlap. An error in the designation of corresponding points leads to an error in the construction of a spatial geometrical relationship, resulting in a deterioration in the accuracy of a stereoscopic display image. See U.S. Pat. No. 6,501,848.